Open-hole gravel packing may be performed after running a sand control screen assembly to an objective depth inside an uncased section. Many times, this technique faces some challenges mainly in deep water surroundings where the annulus sand screen and open hole may experience collapsed sections, high leak-off zones, or fractures.
An “alternate path technique” (shunt tube) has been developed to achieve a complete gravel pack, which is crucial for these high cost wells to bypass any bridge that may form in the annulus. This gravel packing technique needs a precise fluid that can carry gravel particles or proppant using an alternate path.
Typically, non-aqueous fluid (NAF) is used when drilling through productive shale sections. Once the open hole is in place, displacing the NAF to completion brine in presence of sensitive shale can avoid the screens from reaching the required total depth. Running the screens in NAF can significantly increase the chances of a successful screen installation into the open hole. A gravel packing fluid that has the requisite carrying properties and which is compatible with the NAF is used in a technique referred to as non-aqueous fluid packing (NAFPac) when dealing with shale formations.
Lowering the density of the fluid is a way of reducing the overbalance pressure and is an important control to use when dealing with a low operating pressure envelop or when operating near low pressure boundaries.